1. Field of the Invention
The present invention relates to nonwoven fabrics.
2. Related Art
Conventionally, nonwoven fabrics are used in a wide variety of fields, for example, hygiene products such as paper diapers and sanitary napkins, cleaning products such as wipers, and medical products such as masks. In this way, the nonwoven fabrics have been used in various fields. For practical use in products in each field, however, the nonwoven fabrics are required to be produced so as to have characteristics and structures suited to the application of each of the products.
The nonwoven fabrics are formed, for example, by forming fiber layers (fiber webs) by means of a dry method, a wet method or the like, then bonding the fibers that constitute the fiber layers to each other by means of a chemical bond method, a thermal bond method or the like. Such a process of bonding the fibers that constitute the fiber layers, includes a method in which a plurality of needles are repeatedly inserted into the fiber layers and a method in which physical force, such as a water jet stream, is externally applied to the fiber layers.
However, these methods simply help to entangle the fibers with each other and do not adjust the orientation or the arrangement of fibers in the fiber layers or shapes of the fiber layers. In other words, what is produced by means of these methods is merely a sheet-like nonwoven fabric.
A nonwoven fabric with openings is also proposed. To provide openings for a nonwoven fabric, a method is proposed in which a spatial opening is provided by inserting the nonwoven fabric between a mold, having projections such as outwardly projecting needles, and a supporter, which receives the projections and then penetrating the projection portion into the nonwoven fabric (e.g. see Japanese Patent Laid-Open Publication No. H6-330443.)
However, such a nonwoven fabric, if a fiber assembly constituting the nonwoven fabric is included between a projection portion and a receiving-side supporter, will have undulations or openings therein. Therefore, fibers at a wall surface of a projection portion and an opening peripheral edge are compressed, so that a fiber density becomes higher and further is sometimes filmed during generation of nonwoven fabric by heating.
Therefore, when such a nonwoven fabric is used in a surface sheet of an absorbable product or the like, the projection portion, which has a high fiber density, and the opening peripheral edge or the filmed opening peripheral edge may become resistant to liquid absorption. As a result, if a large amount of liquid is transferred to the projection portion or the opening peripheral edge, the liquid gathers on the nonwoven fabric, and hence may soil the skin of a user and make him/her uncomfortable.